1. Field of the Invention
The present invention relates to an electroluminescent (EL) display device and a method of fabricating the same and, more particularly, to an EL display device, which includes a pixel defining layer with at least one barrier layer to reduce the amount of outgas from the pixel defining layer and prevent the degradation of an emission portion due to the outgas, and a method of fabricating the same.
2. Description of the Related Art
Thin and lightweight portable display devices that quickly process a great deal of information are being rapidly developed as the demand for prompt and accurate information increases. Conventional cathode ray tubes (CRT) are heavy, take up a lot of space, and consume a lot of power, and a liquid crystal display (LCD) is complex to manufacture, it has a narrow viewing angle, and it has technical limits in contrast ratio and scaling-up.
On the other hand, an organic EL display device is a self-emissive device in which electrons and holes recombine in an organic emitting layer to generate light. Therefore, not only may the organic EL display device be made lightweight and thin, it may be made with a simpler process since a separate light source is not required unlike an LCD. Furthermore, the organic EL display device has as fast a response speed as a CRT and consumes less power than the CRT. Consequently, the organic EL display device is being considered as a primary next-generation display.
FIG. 1 is a plan view showing a pixel consisting of red (R), green (G) and blue (B) unit pixels of a conventional electro luminescent display device.
Referring to FIG. 1, scan lines 1 may be arranged in a row direction, data lines 2 may be arranged in a column direction and insulated from the scan lines 1, and common power supply voltage lines 3 may be arranged in the column direction, insulated from the scan lines 1 and parallel to the data lines 2. Accordingly, the scan lines 1, the data lines 2 and the common power supply voltage lines 3 define a plurality of unit pixels, such as, for example, R, G, B unit pixels.
Each unit pixel may comprise a switching thin film transistor (TFT) 5, a driving TFT 6, a capacitor 7, and an organic light emitting diode 9.
In each unit pixel, data signals from the data lines 2 according to scan signals from the scan lines 1, for example, electric charges according to a difference between a data voltage and a voltage from the common power supply voltage lines 3, accumulate in the capacitor 7, and signals by the electric charges accumulated in the capacitor 7 are input into the driving TFT 6 through the switching TFT 5. Subsequently, the driving TFT 6 receives the data signals and sends electrical signals to a pixel electrode 8, so that the organic light emitting diode 9, which comprises an organic emission layer formed between the pixel electrode 8 and an opposing electrode, emits light.
FIG. 2 is a cross-sectional view showing an organic light emitting diode in an organic EL display device taken along line I-I′ of FIG. 1.
Referring to FIG. 2, a substrate having R, G, and B unit pixels is provided.
A pixel electrode 8 may be formed on the substrate 10. Then, a pixel defining layer 12 is formed on the entire surface of the substrate 10 having the pixel electrode 8 to define a pixel region where an emission layer will be formed.
Here, the pixel defining layer 12 is generally formed of a photosensitive material. An opening part 11 exposing a part of the pixel electrode 8 may be formed by a photolithography process on the pixel defining layer 12.
After forming the opening part 11, the pixel defining layer 12 may be hardened at temperature of about 230° C. to 280° C. by baking to remove outgas remaining in the pixel defining layer 12.
An organic layer 13 including at least an organic emission layer may be formed on the surface of the substrate 10 having the opening part 11, and an opposing electrode 14 may then be formed on the organic layer 13 and sealed, thereby completing fabrication of the organic EL display device.
In addition to the organic emission layer, the organic layer 13 may further include at least one of a hole injection layer, a hole transport layer, a hole blocking layer, an electron transport layer, and an electron injection layer
However, the outgas cannot be completely removed even though the pixel defining layer 12 is hardened. Furthermore, short-term or long-term chemical decomposition may continuously generate outgas in the pixel defining layer 12.
The outgas may cause pixels to shrink, and it may lower the life cycle of an organic EL display device by deteriorating the organic emission layer. Furthermore, at high temperatures, a material in the pixel defining layer 12 can be decomposed into various molecules including functional groups. The functional groups may change the chemical structure of the organic emission layer, thereby negatively affecting the light emitting function of the organic emission layer, which may deteriorate the device's luminance and color purity.
While an inorganic layer may be used as the pixel defining layer 12 in order to solve the foregoing problems, the inorganic layer may complicate the fabrication process.